By a well is meant a well which has been drilled into the ground, either on land or on a seabed. By a petroleum well is meant a well which has been drilled for the recovery of either gas or oil or both. A petroleum well may produce gas, oil or both, or the well may have the purpose of increasing the recovery of petroleum, for example by giving pressure support to a petroleum reservoir.
A well or petroleum well requires maintenance over the life of the well. Examples of such maintenance work include perforating the production tubing in gas- and oil-producing zones; cementing the annulus; setting plugs and packers; removing sand, sediments and deposits; activating and shutting valves; deploying pumps; and cutting and removing production tubing and casing. Such work may further include logging the well. It is known that such maintenance may be carried out as so-called light well intervention. For each of the different tasks, a suitable tool has been developed, which is lowered into or run into the well.
Light well intervention includes so-called wireline equipment and so-called coiled tubing. A wireline tool is lowered into the well inside a production tubing or its equivalent, hanging on a wire. The wire may be a spun wire or a smooth wire which is termed a slickline in the art. The wire also includes an electrical cable for transmitting electrical energy and cables for transmitting control signals and acquired data. At its end portion, the wire may be provided with a weight. The wire may be used in vertical wells and in wells deviating somewhat from the vertical, as only gravitational forces are acting on the weight and/or the tool. To remedy one of the drawbacks of wire operations, self-propelled tractors have been developed, which are attached to the end portion of a wire.
The electrical conductor supplies the tractor with energy so that it may move, by wheel drive or crawler drive, in wells that have been drilled with deviation, like horizontal wells. The tractor pushes the tool in front of itself down or into the well. Wireline equipment has the advantage of being relatively light-weight, taking up little space and being quick to mobilize and demobilize. One drawback to known wireline equipment is that it cannot convey or carry gas or liquid.
Coiled tubing is fed down the well inside the production tubing or its equivalent. The coiled tubing will extend from the desired location in the well, where the lower portion of the coiled tubing is positioned, up to the surface. The coiled tubing may thus be several thousand meters long. At its lower end portion, the coiled tubing is provided with a tool which has been selected on the basis of the purpose of the task. The coiled tubing has the advantage, among others, that it can be fed into high-pressure wells, that it can be run into wells with deviations and into wells with horizontal portions. The coiled tubing is hollow and therefore forms a continuous channel from the free end portion of the coiled tubing downhole up to the surface. This enables fluid conveyance through the coiled tubing. The fluid may comprise cement, gas and chemical solutions. Such conveyance of fluids down into the well or up from the well is not possible with wire operations or with a wire and tractor. A drawback to coiled tubing is that the equipment is relatively heavy, the equipment requires a derrick over the well head, and it takes time to mobilize and demobilize the equipment. Another drawback is that a fluid flowing through a coiled tubing is exposed to greater friction because of the smaller inner diameter of the coiled tubing compared with the inner diameter of the surrounding production tubing.
The patent document U.S. Pat. No. 5,337,821 discloses an apparatus for measuring flow rates in a reservoir in the ground and the production capacity of the reservoir, among other things. The apparatus is lowered into a well in the ground by means of a logging cable. The apparatus includes lower and upper inflatable packers which, between them, isolate a zone which is to be tested. The apparatus is provided with openings in the isolated zone, openings above the upper packer and an internal channel between the openings in the isolated zone and the openings above the upper packer. A pump may displace a fluid from the zone between the packers to an area above the upper packer through the internal channel. A chamber for sampling a fluid sample is shown as being positioned below the lower packer. The chamber is in fluid communication with the isolated zone. The chamber is not in fluid communication with the well below the lower packer. When the packers of the apparatus have been sealingly activated, there is no fluid communication between the well below the lower packer and the well above the upper packer, nor any fluid communication between the well below the lower packer and the isolated zone.